1. Field of the Invention
The present invention generally relates to an apparatus and method for coating an elongate web, such as a multi filament web, with a substantially uniform coating of a resin or other flowable material along the length of the web.
2. Description of the Related Art
The impregnation of web and sheet-form materials with a wide variety of coating materials, as for example resinous materials of various types, is well known and established in the art.
A primary problem experienced in coating web materials with resin formulations is the difficulty of accurately controlling the amount and uniformity of thickness of the resin applied to the web material, since the uniformity of the applied material and its thickness are often critical in terms of the cost, efficacy and appearance of the of the final product.
Spraying application techniques frequently cannot be employed to coat the web, because the area of extent of the web is such that multiple coating spray heads are required to cover the entire area and the overlap and interference between the spray patterns of the respective heads cause non-uniformity of thickness which is unacceptable in the final coated web product. Alternatively, if a spray head of sufficient spatial "throw" capacity to cover the entire web is employed, there is significant losses of the coating material at the margins of the web, and such losses are in fact also present when multiple spary heads are utilized. These losses not only lower the efficiency of the process in terms of the amount of the originally provided coating material which is used, but present significant effluent disposal and/or recycling problems.
In view of these problems, and in instances where is it desired to coat an elongate web in a continuous process, wherein the web is translated through the process system from a supply roll or other source, to a take-up roll or other collection means, it is advantageous to utilize a transfer roll arrangement, in which a rotating drum is partially immersed in a supply vessel containing a volume of the coating material, as a "bath" of the coating material which then is contacted by the circumferential surface of the transfer roll to transfer coating material from the bath to such surface. With continued rotation of the transfer roll, the resin-beating surface is presented at an upper portion of the rotation path, where it is contacted with the continous web, to effect transfer to the web of the resin material from the surface of the roll.
Although such transfer roll process achieves significantly reduced levels of material losses relative to spray processes, it nonetheless is frequently difficult to accurately and reproduceably control the amount and thickness of the coating material which is applied by the transfer roll. The art therefore has continued to seek improved means and methods for improving the transfer roll process system.
U.S. Pat. No. 5,368,893 issued Nov. 29, 1994 to H. Sommer et al. discloses a coating device which includes a transfer roll engaging a web and transferring coating material to it from a source reservoir. In the disclosed apparatus, a roller squeegee bar formed with a rotating peripheral surface including a plurality of peripheral rises and recesses, bears against the surface of the transfer roll. An air blade downstream of the transfer roll controls final thickness of the coating material on the web. Because the air blade acts so far downstream from the transfer roll, material that is excess must be recirculated in order to reach the transfer reservoir. In addition, no control over the amount of coating material applied to the web exists during the actual transfer of the coating material (from the transfer roll) except as provided by the fixed squeegee bar.
U.S. Pat. No. 4,267,007 issued May 12, 1981 to C. W. Kellogg describes a device for resin application to a multi filament web using a transfer roll. The apparatus disclosed in this patent comprises a mandrel, means for rotatably mounting the mandrel, positioned parallel and in space relationship to the mandrel, and a reciprocating carriage. Variable speed rotation means couple the drive to the mandrel, and effect reciprocation of the carriage at a selected velocity.
While there are guide rolls upstream mad downstream of a transfer roll in the Kellogg system, they are fixedly positioned and no means are provided for adjusting the web angle or the amount of coating material applied to the web. Further, no structure or elements are provided for controlling the amount of resin on the transfer roll.
U.S. Pat. No. 4,672,705 issued Jun. 16, 1987 to H. Bors, et al. describes a transfer roll process system in which a guide roller is placed upstream of the transfer roll. The roll is counterweighted but cannot be adjusted to vary the angle of web contact and to control the amount of coating material applied to the web. Further, such system provides no control of the amount of coating material on the transfer roll.
U.S. Pat. No. 4,048,952 issued Sep. 20, 1977 to Glenn E. Peterson, et al. describes apparatus for inking fabric webbing utilizing a transfer roll, two fixed guide rolls, and a fixed doctor blade, but no other means for controlling the amount of ink applied to the fabric.
U.S. Pat. No. 3,186,861 issued Jun. 1, 1965 to J. W. Smith et al. discloses a process system for producing pressure sensitive record paper in which a guide bar is positioned in proximity to the applicator roll. The coated paper is passed around a backing roll and is acted on by an air knife which removes the excess coating material which collects in an underlying pan, from which it can be recycled to the supply pan feeding the transfer roll.
Accordingly, it is an object of the present invention to provide an improved transfer roll system for coating of webs, which provides effective and accurate adjustability of the amount of coating material applied to the web from the transfer roll and which comprises means to readily adjustably control the angle of contact of the web against the transfer roll to thereby further control the amount and rate of uptake of coating material being applied to the web.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.